Hitherto, as recording materials for recording using beams having a high energy density, such as a laser, etc., there have been used various materials including silver halide photosensitive materials. One such material is a recording material comprising a recording layer having high optical density where information is recorded when a beam having a high energy density is applied, i.e., where irradiated areas are locally heated to undergo a change such as melting, evaporation, aggregation, etc., whereby a difference in optical density results between irradiated areas and nonirradiated areas.
Generally, recording on such a thermal recording material is carried out by converting information to be recorded into an electric time series signal and scanning the recording material with a laser beam whose intensity is modulated according to the signal. This provides the advantage of a real time recording.
Such recording materials have been described in, for example, "Electron, Ion and Laser Beam Technology" by L. Levene et al., records in 11th Symposium (1969); "Electronics" page 50 (Mar. 18, 1968); "The Bell System Technical Journal" by D. Maydan, vol. 50, 1761 (1971); and "Sciene" by C. O. Carlson, vol. 154, 1550 (1966).
In many of these recording materials, a metal film is formed on a transparent plastic base by evaporation or sputtering, etc. Such materials have excellent properties as a thermal recording material, for example, images having a high resolving power can be recorded with high contrast.
As the transparent plastic base, plastic films of polymethyl methacrylate, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polyamide, polystyrene, polyethylene, cross-linked polyethylene or polypropylene, etc. have been used.
In these recording materials, however, the thermal recording layer particularly deteriorates with the passage of time due to moisture or oxygen in the air to form pinholes or reduce the optical density. In particular, since the formation of pinholes of even a few micron size markedly reduces the commercial value of optical discs using the thermal recording layer, higher storability is required for the optical discs as compared to conventional thermal recording materials. Therefore, it has been proposed to provide a protective layer composed of an organic material on the recording layer or to provide air-sandwich recording materials where two recording elements having a thermal recording layer provided on a plastic base are provided such that the recording surfaces face each other through an air layer. However, the deterioration of the recording layer with the passage of time cannot be satisfactorily prevented, because moisture and oxygen pass through the plastic base.